Fuel may be injected to an internal combustion engine so that the engine may provide a requested or desired torque. The amount of fuel injected to the engine may be different than an amount of fuel commanded to be injected to the engine. Further, the amount of fuel requested to be injected may be different than an amount of fuel that provides a desired engine air-fuel mixture ratio. The fueling differences may result from engine component tolerance variation, sensor measurement errors, and errors in open loop fuel control parameters. An estimate of engine air-fuel ratio may be determined via an oxygen sensor, and the engine air-fuel ratio may be fed back to an engine controller to compensate errors between a desired engine air-fuel ratio and a measured air-fuel ratio. The controller may determine an engine air-fuel ratio error by subtracting the measured engine air-fuel ratio from the desired engine air-fuel ratio. The engine air-fuel ratio error may be multiplied by a gain (e.g., real number) to correct the engine air-fuel ratio error. If the value of the gain is small, a long period of time may be needed to drive the engine air-fuel ratio error toward a value of zero. However, if the gain is made too large, the engine air-fuel ratio may be driven to oscillate about the desired engine air-fuel ratio. The oscillations may increase engine emissions and degrade vehicle drivability.
The air-fuel oscillations may be related to a fuel injection delay time between when the fuel is injected to a cylinder and a time when its combustion byproducts are converted into an engine air-fuel ratio via the oxygen sensor and a transfer function. The fuel injection delay time may include but is not limited to the time between fuel injection and combustion of fuel within the cylinder. The delay may also include the amount of time it takes the engine to rotate through the exhaust stroke of the cylinder receiving the fuel and release exhaust gases from the cylinder into the exhaust manifold as well as an amount of time it takes the exhaust gases to travel from the exhaust valves of the cylinder to the oxygen sensor in the exhaust manifold. The delay time may cause the controller to observe no change in engine air-fuel ratio when the engine air-fuel may have already changed. Consequently, the controller may attempt to increase the control action (e.g., amount of fuel injected) to drive the measured engine air-fuel ratio closer to the desired engine air-fuel ratio. However, since the engine air-fuel ratio already changed due to earlier control adjustments, the engine air-fuel ratio may be overdriven, thereby causing the controller to over compensate in a reverse direction, which may induce the engine air-fuel ratio oscillations.
The fuel injection delay time may be empirically determined via adjusting an air-fuel ratio of engine cylinders at a steady state engine speed and recording an amount of time it take to observe a change in the engine air-fuel ratio. The delay value may be stored in memory where it represents fuel injection time delay for each engine cylinder. The fuel injection delay value may be applied in a controller compensation network to allow for increased gain while reducing the possibility of engine air-fuel ratio oscillations. However, recent developments have enabled each cylinder of an engine to be activated and deactivated independent of other cylinders to increase engine efficiency and provide a desired amount of torque. Further, the cylinders may be activated and deactivated in many different combinations to maintain cylinder temperature and reduce engine oil consumption. As a result, a single value for the fuel injection delay estimate for a particular engine speed and load may no longer be appropriate. Therefore, it may be desirable to provide a way of determining fuel injection delay for an engine having cylinders that may be deactivated.
The inventors herein have recognized the above-mentioned issues and have developed an engine control method, comprising: injecting fuel to an engine via a controller in response to a fuel injection delay produced via a weighted average of a fuel injection delay of a past engine cycle and a fuel injection delay of a present engine cycle.
By adjusting a fuel injection delay based on a weighted average of a fuel injection delay of a past engine cycle and a fuel injection delay of a present engine cycle, it may be possible to provide the technical result of an improved estimate of fuel injection delay when it is unknown whether or not one or more cylinders of a cylinder bank will be deactivated (e.g., cessation of combustion and fuel injection to the engine cylinder) in the near future. Incorporating past fuel injection delays and present fuel injection delay into an estimate of future fuel injection delay provides a reasonable estimate of future fuel injection delays when past cylinder deactivation patterns are correlated to future cylinder deactivation patterns. In cases where a future cylinder deactivation pattern is known, the fuel injection delay may be determined via adding a base cylinder delay time to an extra delay time that is based on the expected cylinder deactivation pattern. In these ways, whether or not a future cylinder firing pattern is known, an estimate of fuel injection delay may be determined.
The present description may provide several advantages. In particular, the approach may provide improved fuel injection control by permitting higher gains so that fuel injection errors may be reduced in a more timely manner. Further, the approach provides for estimating fuel injection delay whether or not a future cylinder firing pattern is known. In addition, the approach may provide improved air-fuel control for engines that may deactivate engine cylinders in a large number of different patterns.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.